Messages in this thread | | | Date | Sat, 12 Jan 2008 19:56:01 -0600 | From | Robert Hancock <> | Subject | Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driver opt-in |
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Linus Torvalds wrote: > > On Fri, 11 Jan 2008, Matthew Wilcox wrote: >> Did I miss a bug report? The only problems I'm currently aware of are >> the ones where using MMCONFIG during BAR probing causes a hard lockup on >> some Intel machines, and the ones where we get bad config data on some >> AMD machines due to the configuration retry status being mishandled. > > Hmm. Were all those reports root-caused to just that BAR probing? If so, > we may be in better shape than I worried.
As far as I'm aware, the known MMCONFIG-related issues that I'm aware of are or have been:
-Some devices built into the AMD K8 integrated northbridge can't be reached by MMCONFIG - already handled
-Overlap of device BAR and MMCONFIG aperature during BAR sizing causing lockup - can be avoided by disabling device decode during BAR sizing.
-PCI Express CRS-related issues - already handled by disabling CRS by default
-Devices behind certain host bridges (some AMD HT to PCI-X bridges, others?) can't be reached by MMCONFIG - can be handled by Tony Camuso's patch or something similar (note that this is really a BIOS bug, it should not list those buses in the MCFG table if MMCONFIG cannot access them, and if it didn't I think we could already handle that)
-Some issue with some AMD CPUs needing MMCONFIG accesses to use a certain register I believe? already handled?
Of these, I think the PCI BAR/MMCONFIG overlap problem is responsible for by far the most cases of machines thought to have "broken MMCONFIG", when in fact they were nothing of the sort. I don't recall hearing of a single machine where MMCONFIG really just didn't work at all.
As I've mentioned before, all of these issues (well, I suppose not the BAR overlap one) need to be resolved whether we have Arjan's patch or not, otherwise if a driver does opt in and tries to use extended config space it will still break. And if they are resolved, the patch seems quite pointless.
-- Robert Hancock Saskatoon, SK, Canada To email, remove "nospam" from hancockr@nospamshaw.ca Home Page: http://www.roberthancock.com/
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